“The terror is over,” the Boston Police Department announced via Twitter just minutes after the dramatic Friday night capture of Dzhokhar Tsarnaev.

If only that were the case. Instead, the Boston Marathon bombings were a stunning reminder of America’s vulnerability despite the post-9/11 antiterrorism efforts of local, state and federal law enforcement agencies.

Many vexing questions remain, including what the FBI knew about Tamerlan Tsarnaev and his younger brother and when. And was the agency at a disadvantage because the Russian government was less than forthcoming in warnings that prompted Tsarnaev’s questioning in 2011, as news reports have suggested?

One risk is that the marathon bombings will now become so politicized that federal authorities themselves will be less than fully transparent.

Without so much as a single hearing, Rep. Michael McCaul, R-Texas, who heads the House Homeland Security Committee, and committee member Rep. Peter King, R-N.Y., already have labeled the FBI’s handling of the case “an intelligence failure.”

Certainly any act of terrorism that kills three people and injures more than 180 is a security breakdown, and obviously the FBI did not prevent the attack even though Tamerlan Tsarnaev had raised some level of suspicion in Russia.

REQUEST FROM RUSSIA

“Once the FBI learned the identities of the two brothers today, the FBI reviewed its records and determined that in early 2011, a foreign government asked the FBI for information about Tamerlan Tsarnaev. The request stated that it was based on information that he was a follower of radical Islam and a strong believer, and that he had changed drastically since 2010 as he prepared to leave the United States for travel to the country’s region to join unspecified underground groups.”

Source: An April 19 statement by the FBI

But without more information from federal authorities — and the Russians — we can only speculate about how the attack could have been thwarted and what of value we might be able to learn from Boston.

For starters, we need to know how and when the brothers were radicalized. We may learn that Tamerlan Tsarnaev’s 2012 trip to Dagestan, a Russian republic bordering Chechnya, was a tipping point in what his family members said was a dramatic turn toward radical Islam.

At the request of the Russian government, FBI agents talked to Tamerlan Tsarnaev before the trip but were not concerned and closed their files after giving their findings to the Russian government, the Wall Street Journal reported Monday.

According to an unnamed senior U.S. official cited by the New York Times, U.S. authorities asked the Russians for more information about their interest in Tsarnaev at the time but were told only that he was viewed as a risk to join underground groups.

In post-9/11 America, federal authorities are flooded with tips on possible terrorism links, many of which lead nowhere. It’s also not unusual for foreign governments to make requests for information like the one that came from Russia.

It’s not clear if the older Tsarnaev brother received training in explosives or other instruction during the six-month trip. We still don’t know if the Russian investigators who contacted U.S. authorities monitored his activities in Dagestan.

Security experts said the brothers could have been influenced by a group or individuals in Boston, or through Internet communication. It’s also possible they were motivated by exposure to jihadist websites. Self-radicalization — a growing concern in global security — cannot be ruled out.

“There have to be U.S. factors involved,” said Prof. Joseph Young, a terrorism expert at American University in Washington, D.C., although he added that the separatist uprising in Chechnya likely influenced the Tsarnaevs.

He noted that as many as 20 young Somali-American men from Minnesota have been recruited by the terrorist group Al-Shabab to return to Somalia to fight in that country’s civil war.

With so many unanswered questions in the Boston attack, it’s too soon to say whether the FBI should have been able to prevent it, said John Patrick Egelhof, a private investigator and retired FBI agent who now lives in Bemidji, Minn.

Security risks are a given in a free society, and the only certain prevention is unacceptable, Egelhof said. “We could solve all of this immediately if we wanted to become a police state,” he added.

Young said Americans need to come to terms with the fact that terrorism has existed since biblical times, and more attacks are likely. “I think it’s a little overblown to say [federal authorities] have to get this right 100 percent of the time,” Young said.

What they do have to get right is the postattack analysis, especially if it can help minimize future exposure to terror. That starts with facts — and those are still in short supply in the wake of the marathon bombings.